U.S. Pat. No. 4,945,327 describes a molded case circuit breaker having a steady state ampere rating of up to 1200 amperes. The circuit breaker operating mechanism is designed for current-limiting wherein the circuit current is interrupted in the early stages of the current waveform to reduce the current let-through during circuit interruption under intense overcurrent conditions. Compact arc chambers are also disclosed for handling the large amount of arc exhaust gases generated during such current-limiting circuit interruption.
The advent of electronic trip circuits in the form of a printed wire board mounted within the circuit breaker cover has been met with immediate commercial success. A circuit breaker of uniform geometry employing an electronic trip unit is adapted for a wide range of circuit breaker ampere ratings by selection of an ampere rating plug that is either factory or field-installable.
A so-called "basic" electronic trip circuit in the form of an integrated circuit contained within a compact printed wire board is described within U.S. Pat. No. 4,589,052. The trip unit is capable of predetermined circuit interruption under so-called "long time", "short time" and "instantaneous" overcurrent conditions. External adjustment to the trip unit circuit to set the circuit overload current values and the associated time delays is made by means of rotary switches mounted on the circuit breaker cover.
U.S. Pat. No. 4,870,531 and 4,945,443 disclose more advanced electronic trip units whereby the circuit overload current values and time delays are adjusted by means of a keypad and display unit mounted within the circuit breaker cover. The more advanced circuitry provides metering and control function along with basic overcurrent protection.
To allow for the customer-selection of the different overcurrent trip units, it would be desirable to use a uniform circuit breaker design capable of accepting either of the two electronic circuits available.
Accordingly, one purpose of the instant invention is to provide an industrial-rated circuit breaker where the trip unit can be selected and field-installed without requiring modification to the circuit breaker enclosure. Three current transformers are used with the electronic trip units to determine the circuit current and provide such information to the trip units. U.S. Pat. No. 4,281,359 describes the assembly of the electronic trip unit on the current transformers with the load terminal connectors passing through the current transformers to form the primary winding.
The provision of the current transformers at the load terminal end of the circuit breaker enclosure raises the height requirements of the load terminal lug that connect with the circuit breaker load terminals somewhat higher than the lugs used for connecting with the line terminals at the line terminal end of the circuit breaker.
Accordingly, a further purpose of the invention is to provide a transformer load terminal assembly capable of accepting the same-sized lugs that are used at the line end of the circuit breaker.